1. Field of the Invention
The present invention relates to a leak detection system and, more particularly, to a pneumatic leak detection system for use in a manufacturing process to check parts and assemblies for leaks.
2. Description of Related Art
Pneumatic leak detection systems are commonly used in manufacturing processes to check parts and assemblies for leaks around joints, gaskets and welds, as well as for porosity in castings, and as an overall quality test. This requires that the test be conducted in the shortest time possible to reduce manufacturing time and cost.
Two pneumatic leak detection systems commonly used include the pressure decay leak test system and the dynamic or mass flow leak test system. Current pressure decay systems employ up to three different periods to test a part. These periods are usually referred to as fill, stabilize and test times, and each time period has a unique function. During the fill time period, the part is pressurized or charged by a pressure source to a value above the test pressure, and the pressure source is then removed or a valve is closed to initiate the stabilize time period.
As the part is pressurized during the fill period, the air undergoes adiabatic heating, and as the air then cools, the pressure within the part drops. The pressure within the part eventually stabilizes at some lower pressure, which is the test pressure if the test process is carried out correctly and there are no leaks. After the stabilization period, the part enters the test period where additional time is allowed for the pressure to drop, for example, if there is a leak or other defect in the part. At this time, a decision may be made as to whether to accept or reject the part.
In the mass flow leak test system, a pressure is maintained on the part from a pressure source throughout the test, and make-up air for compensating for any leaks while maintaining a predetermined pressure on the part is measured by a flow meter. If there is no leak, then no make-up air will be required. However, if there is a leak, then a certain mass flow of air will be required, which air is directed through the flow meter for accurately determining the magnitude of the leak. In this type of system, the stabilize period is normally eliminated and the fill and test phases overlap. In other words, as the pressurized air within the part cools after the initial fill, make-up air is provided and the flow to the part eventually stabilizes to either a no leak condition or to a steady state flow indicating the presence of a leak.
Typically, the termination of one of the test periods and the start of the next period is controlled in accordance with a preset time for each phase. For example, the time period for each phase may be set by using the test system to test a part which is known to have no defects whereby the required time for filling the part, for stabilizing the pressure in the part and for obtaining a test result may be determined. The actual times required for filling, stabilizing and testing the part are subject to variations in the ambient conditions of the environment surrounding the part, such as temperature and part variations, and as such can vary from day to day. Thus, the time periods for the different phases for testing the part may actually be too long or too short depending on variations in the conditions under which the part is tested.
Accordingly, there is a need for a leakage test apparatus and method which is capable of testing a part in the least amount of time necessary. In addition, there is a need for such an apparatus and method wherein the different phases of the testing are not regulated by preset time periods and wherein the start of each successive phase of the testing procedure occurs in response to a measured condition occurring during a prior phase of the testing procedure.